When a surgical operation is effected on the chest of a patient, an extracorporeal blood circulation circuit including an artificial lung is used in recent years in bypassing relation to the lung of the patient, and carbon dioxide is removed from the blood of the patient and fresh oxygen is added to the blood by the artificial lung.
The extracorporeal blood circulation circuit includes a blood reservoir for temporarily storing the blood so that air bubbles produced during the circulation of the blood will be removed from the blood, or for supplying stored blood to make up for a reduction in the rate of circulation of the blood. Blood reservoirs now in use in the art are roughly classified into a soft bag type which is made of a soft material, and a hard shell type which is made of a hard material. The soft bag reservoir is advantageous in that it has no blood-air interface, but disadvantageous in that it cannot hold a large amount of blood and cannot give an exact indication of how much blood is stored therein.
The hard shell reservoir can store a large amount of blood and allows the user to know the exact amount of blood stored therein. Other advantages of the hard shell reservoir are that it can easily be united with an artificial lung, thus permitting an extracorporeal blood circulation circuit to be simplified, and also the blood can easily be debubblized when the extracorporeal blood circulation circuit is set up and primed. Japanese Laid-Open Patent Publication No. 59(1984)-57661, for example, proposes a hard shell blood reservoir combined with an artificial lung.
It is very important that a hard shell blood reservoir be capable of reliably removing air bubbles which have been introduced into the blood through a blood extracting tube. If the blood containing air bubbles were returned to the patient, then the patient would suffer from the danger of embolism. The hard shell blood reservoir therefore has a debubblizer for removing air bubbles from the stored blood.
One known hard shell blood reservoir with a debubblizer, which is combined with an artificial lung, is a blood reservoir LPM 50 (manufactured by Baxter Travenol Laboratories, Inc.) as shown in FIG. 1 of the accompanying drawings. The blood reservoir, denoted at 2, has a blood debubblizer 8 disposed in a blood inlet chamber 6 near a blood inlet port 4 and held in contact with the bottom of the blood inlet chamber 6. Blood B which has been introduced from an artificial lung 10 through a heat exchanger 12 into the blood reservoir 2 flows into a blood storage chamber 14 without being subjected to a large resistance by the debubblizer 8. Since the blood B is not kept in effective contact with the debubblizer 8, the debubblizer 8 fails to debubblize the blood B effectively. Air bubbles, particularly small air bubbles, contained in the blood B therefore tend to be carried into the blood storage chamber 14 by the flow of the blood B.